A flow cytometer for use in medical and biological fields includes a fluorescence detecting device that receives fluorescence emitted by a fluorochrome in a measurement object irradiated with laser light and identifies the kind of the measurement object.
More specifically, in the flow cytometer, a suspension liquid containing a measurement object such as a biological material (e.g., cells, DNA, RNA, enzymes, or proteins) labeled with a fluorescent reagent is allowed to flow through a tube together with a sheath liquid flowing under pressure at a speed of about 10 m/sec or less to form a laminar sheath flow. The flow cytometer receives fluorescence emitted by a fluorochrome attached to the measurement object by irradiating the measurement object in the laminar sheath flow with laser light and identifies the measurement object by using the fluorescence as a label.
The flow cytometer can measure, for example, the relative amounts of DNA, RNA, enzymes, proteins, etc. contained in a cell and can quickly analyze their functions. Further, a cell sorter or the like is used to identify a predetermined type of cell or chromosome based on fluorescence and selectively and quickly collect only the identified cells or chromosomes alive.
The use of such a cell sorter is required to quickly and accurately identify more kinds of measurement objects from information about fluorescence.
Patent Document 1 discloses a fluorescence detecting device and a fluorescence detecting method which are capable of accurately and quickly identifying many kinds of measurement objects by calculating the fluorescence lifetime (fluorescence relaxation time) of fluorescence emitted by a measurement object irradiated with laser light.
Patent Document 1 describes that a fluorescence relaxation time is calculated from the phase delay of a fluorescent signal of fluorescence emitted by a measurement object irradiated with intensity-modulated laser light with respect to a modulation signal used for modulating the intensity of laser light.